1. Field of the Invention
The invention relates to hybrid laminate composites, and in particular to composites having alternating layers of dense ceramic and fiber-reinforced ceramic matrix composite (CMC) layers.
2. Description of the Prior Art
Fiber-reinforced ceramic matrix composites (CMCs) are used for high temperature components subject to severe thermal and mechanical loads. The key material property requirements include high failure strain, good damage tolerance and thermal shock resistance, and microstructural stability in oxidizing environments. Resistance to wear and abrasion and high thermal conductivity are also important.
The majority of CMCs developed to date undergo matrix cracking at relatively low stress levels, particularly in cross-ply and woven fiber architectures. Cracking usually begins in the off-axis plies and subsequently progresses through to the 0 plies. The cracks in the 0 plies are accommodated by debonding and sliding along the fiber-matrix interface. It has been recognized that such cracking is necessary in order to achieve high damage tolerance and notch-insensitive behavior. However, the cracks form pathways for oxygen ingress into the composite. For non-oxide CMCs, this invariably leads to oxidation of both the fiber coatings and the fibers, which, in turn diminishes the tensile properties dramatically. See, T. Mah, M. G. Mendiratta, A. P. Katz, R. Ruh and K. S. Mazdiyasni, "High-Temperature Mechanical Behavior of Fiber-Reinforced Glass-Ceramic-Matrix Composites," J. Am. Ceram. Soc. 68 [9] (1985) C-248-C-251.
One object of the invention is to produce hybrid CMC laminates that exhibit good potential for high temperature applications which are not subject to the foregoing defect.
Although the production and properties of laminates is described generally in Lange et.al., "Fiber Reinforced Laminated Ceramic Composites and Method Thereof," U.S. Pat. No. 5,092,948 (1992), Folsom et.al., "Mechanical Behavior of a Laminar Ceramic/Fiber-Reinforced Epoxy Composite", J.Am.Ceram.Soc. 75 [11] at 2969-75 (1992); Folsom et.al., "On the Flexural Properties of Brittle Multilayer Materials I, Modeling", J.Am.Ceram.Soc. 77 [3] at 689-96 (1994a); and Folsom et.al., "On the Flexural Properties of Brittle Multilayer Materials II, Experiments", J.Am.Ceram.Soc. 77 [8] at 2081-87 (1994b), the interface between the sintered ceramic and the fiber layer is crack deflecting or weak, while the fiber layer itself has no mechanism to deflect cracks. Such conditions when extended to high temperature materials do not produce the desired effect.
Therefore what is needed is some way to incorporate a strong sintered ceramic/fiber-reinforced CMC interface and a crack deflecting mechanism with the CMC layer to obtain thermal shock resistance, delayed cracking in the CMC layer to high stress levels.
Further, it is an object of the invention to create larger and more complexly shaped structures which have these improved properties.